PEAR Auth: Duplicate usernames

I'm currently working the Auth package into an application and discovered that it's possible with addUser() to add multiple users with the same username. This seems problematic to me, especially in situations using removeUser(). My application currently distinguishes users by an additional, unique id field, but this is irrelevant to the Auth base class since it operates for the most part on usernamecol and passwordcol. I'm wondering how others have handled this. My initial thoughts are to override either Auth's or the container's addUser() method to incorporate a check ensuring that there's only one record with $this->username, but wanted to make sure there wasn't an easier way before doing that. Andy